While the proposed tie-up is focused on routes between Australia and Europe, Qantas and Emirates have sought to extend it to cover routes across the Tasman.

The airports say a duopoly will be created on trans-Tasman routes because a tie-up between Qantas and Emirates, together with the existing Virgin Australia-Air New Zealand alliance, would give the two groups control of almost 97 per cent of the market.

They warn of an ''increased likelihood of higher prices'' for flights between Australia and New Zealand. The New Zealand Airports Association has called for a ''comprehensive, robust and transparent cost-benefit analysis'' of the effects of approving the deal. If the deal is approved, it wants conditions imposed to ensure Qantas and Emirates live up to their promises of their alliance benefiting consumers.

''It is important to remember that there is no guarantee that these claimed benefits will materialise,'' it said in a submission to the country's Transport Minister. ''Many of the stated benefits would be expected primarily to enhance the marketing position and market share [of Qantas and Emirates].''

Air New Zealand has also raised concerns about the role of Qantas' offshoot, Jetstar, in the proposed alliance, and has opposed the ''open-ended nature'' of the application.

The Qantas-Emirates deal needs approval from regulators in Australia, NZ and Singapore.